1. Field of the Invention
The present invention relates to a zoom lens system.
2. Description of the Related Art
In a zoom lens system of the prior art, contradictory demands for a high zoom ratio and miniaturization are required. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, lens-group-moving paths) are determined (i.e., solutions for lens-group-moving paths) so that the zoom ratio becomes high, interference of the lens group occurs on the telephoto side, or interference of a lens group and the image plane occurs at the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the system cannot be obtained due to the mechanical structure thereof.
It is an object of the present invention to provide a zoom lens system which is miniaturized and has a high zoom ratio.
According to the first aspect of the present invention, in a zoom lens system including a plurality of lens groups being relatively moveable in order to vary the focal length, at least one lens group is arranged to be a lens group (hereinafter, a switching lens group) which includes two or more sub-lens groups, and in which one sub-lens group is made moveable, along the optical axis, with respect to the other sub-lens group. In the first focal-length range of the zooming range of the zoom lens system, the moveable sub-lens group and the other sub-lens group maintain the first distance; and in the second focal-length range which covers the first focal-length range and a range different therefrom, the moveable sub-lens group and the other sub-lens group maintain the second distance which is different from the first one.
In the switching lens group, when the first distance is changed to the second distance, or vice versa, the distances among the switching lens group and other lens groups in the zoom lens system are varied. The number of the lens groups is preferably two or three. In the two-lens-group zoom lens system, the front or rear lens group can be the switching lens group. In the three-lens-group zoom lens system, the intermediate (second) lens group is preferably the switching lens group, though any one of lens groups can be the switching lens group. Furthermore, the switching lens group may function as a focusing lens group.
Also, a plurality of switching lens groups can be provided in the zoom lens system according to the present invention. In this case, a boundary focal length (i.e., a switching point) for changing the first distance to the second distance, may be set equally for all the switching lens groups, or set differently for each switching lens group.
According to another aspect of the present invention, in a zoom lens system including a plurality of lens groups being relatively moveable upon zooming, at least one lens group includes a plurality of sub-lens groups, one of which is made moveable, along the optical axis, to be selectively positioned at one of the extremities of a range within which the moveable sub-lens group is allowed to move, with respect to other sub-lens groups.
In a short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the moveable sub-lens group is arranged to position at one of the extremities.
In a long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the moveable sub-lens group is arranged to position at the other extremity.
Furthermore, the lens-group-moving paths of the lens group containing the plural sub-lens groups, and those of other lens groups are discontinued at the intermediate focal length. The zoom lens system is arranged to correctly form an image on the image plane in accordance with a position of the moveable sub-lens group. Being discontinued hereinafter means a path deflected like saw teeth, unlike a straight or smoothly curved path. Further, forming an image correctly hereinafter means that an image is formed on an image plane which is predeterminedly positioned.
According to still another aspect of the present invention, in a zoom lens system including a plurality of lens groups being relatively moveable in order to vary the focal length, at least one lens group is arranged to be the switching lens group which includes two or more sub-lens groups, and in which one sub-lens group is made moveable, along the optical axis, towards one of the object-side and image-plane-side extremities with respect to the other sub-lens group.
In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the switching lens group and other lens groups are moved towards the object, and the distances thereamong are varied, while the moveable sub-lens group remains stationary at the object-side extremity.
At the intermediate focal length, the moveable sub-lens group is moved to the image-plane-side extremity, and at the same time, the switching lens group and other lens groups are respectively moved towards the image plane.
In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the switching lens group and other lens groups are moved towards the object, and the distances thereamong are varied, while the moveable sub-lens group remains stationary at the image-plane-side extremity.
According to yet another aspect of the present invention, in a zoom lens system including a plurality of lens groups being relatively moveable in order to vary the focal length, a plurality of lens groups are arranged to be the switching lens groups, each of which includes two or more sub-lens groups. In each switching lens group, one sub-lens group is made moveable, along the optical axis, towards one of the object-side and image-plane-side extremities with respect to the other sub-lens group.
At the short focal length extremity, all the moveable sub-lens groups in the switching lens groups are positioned at the object-side extremity.
At a plurality of intermediate focal lengths between the short and long focal length extremities, the moveable sub-lens groups are moved, one by one, from the object-side extremity to the image-plane-side extremity, and at the same time, all the lens groups including the switching lens groups are moved towards the object.
The switching lens groups and other lens groups are moved towards the object in the following zooming ranges, while the distances among the lens groups are varied:
(i) from the short focal length extremity to the first intermediate focal length;
(ii) along a plurality of intermediate focal lengths; and
(iii) from the last intermediate focal length to the long focal length extremity.
All of the plural lens groups of the zoom lens system may be constituted as switching lens groups. In the case where a zoom lens system has two groups, the zoom lens system with a high zoom ratio and a simple structure can be obtained.
Embodiments according to the present invention will be discussed.
The zoom lens system of the first embodiment includes a negative first lens group, a positive second lens group and a negative third lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second and third lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the first, second and third lens groups move towards the object, while the first and second lens groups maintain the first distance therebetween, and while the distance between the third lens group and the integrally moved first and second lens groups is varied;
[B] At the intermediate focal length, the first and second lens groups are moved towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range, and the first distance is made shorter; and the third lens group moves towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range; and
[C] In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the first, second and third lens groups move towards the object, while the second distance, which is shorter than the first distance, between the first and second lens groups is maintained, and while the distance between the third lens group and the integrally moved first and second lens groups is varied.
The zoom lens system of the second embodiment includes a positive first lens group, a negative second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the first, second, third and fourth lens groups move towards the object, while the second and third lens groups maintain the first distance therebetween, and while the distances among the first lens group, the integrally moved second and third lens groups, and the fourth lens group are varied;
[B] At the intermediate focal length, the second and third lens groups are moved towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range, and the first distance is made shorter; and the first and fourth lens groups move towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range; and
[C] In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the first, second, third and fourth lens groups move towards the object, while the second distance, which is shorter than the first distance, between the second and third lens groups is maintained, and while the distances among the first lens group, the integrally moved second and third lens groups, and the fourth lens group are varied.
The zoom lens system of the third embodiment includes a negative first lens group, a negative second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the first, second, third and fourth lens groups move towards the object, while the second and third lens groups maintain the first distance therebetween, and while the distances among the first lens group, the integrally moved second and third lens groups, and the fourth lens group are varied;
[B] At the intermediate focal length, the second and third lens groups are moved towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range, and the first distance is made shorter; and the first and fourth lens groups move towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range; and
[C] In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the first, second, third and fourth lens groups move towards the object, while the second distance, which is shorter than the first distance, between the second and third lens groups is maintained, and while the distances among the first lens group, the integrally moved second and third lens groups, and the fourth lens group are varied.
The zoom lens system of the fourth embodiment includes a negative first lens group, a positive second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the first and second lens groups maintain a longer distance therebetween, and the third and fourth lens groups maintain a longer distance therebetween; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied;
[B] At the intermediate focal length, the first and second lens groups are moved towards the image plane with respect to the long-focal-length side extremity of the short-focal-length side zooming range, and the longer distance therebetween is made shorter; and the third and fourth lens groups move towards the image plane with respect to the long-focal-length side extremity of the short-focal-length side zooming range, and the longer distance therebetween is made shorter; and
[C] In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the first and second lens groups maintain the shorter distance, and the third and fourth lens groups maintain the shorter distance; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied.
The zoom lens system of the fifth embodiment includes a negative first lens group, a positive second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over the first intermediate focal length, the first and second lens groups maintain a longer distance, and the third and fourth lens groups maintain a longer distance; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied;
[B] At the first intermediate focal length, the first and second lens groups are moved towards the image plane with respect to the long-focal-length side extremity of the short-focal-length side zooming range, and the longer distance therebetween is made shorter; and the third and fourth lens groups integrally move towards the image plane;
[C] In an intermediate-focal-length zooming range covering the first intermediate focal length over the second intermediate focal length, the first and second lens groups maintain the shorter distance, and the third and fourth lens groups maintain the longer distance, and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied;
[D] At the second intermediate focal length, the third and fourth lens groups move towards the image plane with respect to the long-focal-length side extremity of the intermediate-focal-length zooming range, and the longer distance therebetween is made shorter; and the first and second lens groups integrally move towards the image plane; and
[E] In the long-focal-length side zooming range covering the long focal length extremity over the second intermediate focal length, the first and second lens groups maintain the shorter distance, and the third and fourth lens groups maintain the shorter distance; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied.
The zoom lens system of the sixth embodiment includes a negative first lens group, a positive second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over the first intermediate focal length, the first and second lens groups maintain a longer distance therebetween, and the third and fourth lens groups maintain a longer distance therebetween; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied;
[B] At the first intermediate focal length, the third and fourth lens groups are moved towards the image plane with respect to the long focal-length-side extremity of the short-focal-length side zooming range, and the longer distance therebetween is made shorter; and the first and second lens groups integrally move towards the image plane;
[C] In an intermediate-focal-length zooming range covering the first intermediate focal length over the second intermediate focal length, the first and second lens groups maintain the longer distance therebetween, and the third and fourth lens groups maintain the shorter distance therebetween; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied;
[D] At the second intermediate focal length, the first and second lens groups move towards the image plane with respect to the long-focal-length side extremity of the intermediate-focal-length zooming range, and the longer distance therebetween is made shorter; and the third and fourth lens groups integrally move towards the image plane; and
[E] In the long-focal-length side zooming range covering the long focal length extremity over the second intermediate focal length, the first and second lens groups maintain the shorter distance therebetween, and the third and fourth lens groups maintain the shorter distance therebetween; and the integrally moved first and second lens groups, and the integrally moved third and fourth lens groups are arranged to move towards the object while the distance therebetween is varied.
The zoom lens system of the seventh embodiment includes a positive first lens group, a negative second lens group, a positive third lens group and a negative fourth lens group, in this order from the object. The entire focal length of the zoom lens system is varied between the long and short focal length extremities by varying the distances among the lens groups. The first, second, third and fourth lens groups are moved along the following lens-group-moving paths:
[A] In the short-focal-length side zooming range covering the short focal length extremity over an intermediate focal length, the first and second lens groups maintain a shorter distance therebetween, and the second and third lens groups maintain a longer distance therebetween; and the integrally moved first, second and third lens groups, and the fourth lens group are arranged to move towards the object while the distance therebetween is varied;
[B] At the intermediate focal length, the second lens group moves towards the image plane, and thereby the distance between the first and second lens groups is made longer, and the distance between the second and third lens groups is made shorter; and
[C] In the long-focal-length side zooming range covering the long focal length extremity over the intermediate focal length, the first and second lens groups maintain the longer distance, and the second and third lens groups maintain the shorter distance; and the integrally moved first, second and third lens groups, and the fourth lens group are arranged to move towards the object while the distance therebetween is varied.
It is practical to apply the zoom lens system of the present invention to a photographing lens system of a camera in which the photographing lens system and a finder optical system are independently provided. It is also practical to employ a plurality of focal-length steps which are determined in a stepwise manner along the lens-group-moving paths.
In the zoom lens system of the present invention, there are discontinuities along the lens-group-moving paths, and the movement of the moveable sub-lens groups is allowed at the intermediate focal lengths. Therefore as explained, the zoom lens system is preferably employed in a camera in which a finder optical system and a photographing optical system are independently provided, since if the zoom lens system were employed in a single lens reflex camera, the discontinuities of the lens-group-moving paths, and the change of an image due to the movement of lens groups are inevitably viewed. Due to the same reasons, positions at which the lens groups stop upon photographing are preferably provided in a stepwise manner along the lens-group-moving paths.
It is noted that, because of the aforementioned discontinuities and varying of distances, the switching lens groups of the invention do not necessarily fit within the ordinary meaning of an xe2x80x9cN lens groupxe2x80x9d system (where N is a whole number).
For example, in the case of a lens having a switching lens group and one xe2x80x9cconventionalxe2x80x9d lens group, the present disclosure characterizes, for the purposes of explanation, such a lens (i) as having a positive lens group (which is a switching lens group) and a negative lens group; (ii) as having a first lens group 10 (a switching lens group with first and second sub-lens groups S1 and S2) and a second lens group 20; (iii) as having negative, positive, and negative lens groups in order from the object; and (iv) as being two different two-lens-group systems for obtaining two different solutions. However, the use of the different characterizations is not inconsistent, and does not mean that a xe2x80x9cswitching lens groupxe2x80x9d according to the invention should be considered to be a conventional xe2x80x9clens groupxe2x80x9d. The use of different characterizations emphasizes that the switching lens groups disclosed herein are different from ordinary xe2x80x9clens groupsxe2x80x9d. As indicated, the same principle applies to the case of a lens having more than one switching lens groups and/or more than one xe2x80x9cconventionalxe2x80x9d lens groups.
Accordingly, the claims and disclosure of the present application should be interpreted to be consistent with the meaning of xe2x80x9clens groupxe2x80x9d; xe2x80x9csub-lens groupxe2x80x9d; xe2x80x9cswitching lens groupxe2x80x9d; and xe2x80x9czooming lens groupxe2x80x9d as set forth herein where such terms would be inconsistent with the same terms as otherwise employed in the art.